WO2020000227A1

WO2020000227A1 - Voltage converter circuit, controlling method and power supplier

Info

Publication number: WO2020000227A1
Application number: PCT/CN2018/092982
Authority: WO
Inventors: Xinhai Li; Yaofeng LIN
Original assignee: Tridonic Gmbh & Co Kg; Yaofeng LIN
Priority date: 2018-06-27
Filing date: 2018-06-27
Publication date: 2020-01-02
Also published as: GB202016959D0; GB2587140A; GB2587140B

Abstract

A voltage converter circuit, a controlling method and a power supplier are provided. The voltage converter circuit includes: a bootstrap gate driver, configured to output a driving signal from a first output port (Ho) according to a controlling signal received from a first input port; a bootstrap capacitor, configured to be connected between a second output port (Vb) and a third output port (Vs) of the bootstrap gate driver; a converting circuit, configured to comprise at least a first switching element, an inductor and a capacitor connecting in serial between an input voltage port and a ground port, an output voltage being outputted from an output voltage port which connects to a first connecting node (A) between the inductor and the capacitor, a gate of the first switching element receives the driving signal; and a first connecting control circuit, configured to be connected between the third output port (Vs) and a second connecting node (B) between the first switching element and the inductor, the first connecting control circuit controls the second connecting node to electrically connect to or disconnect from the third output port, according to a voltage of the second output port. Therefore, the bootstrap capacitor will be charged up in a short time, and the voltage converter circuit will not be latched and startup soon.

Description

VOLTAGE CONVERTER CIRCUIT, CONTROLLING METHOD AND POWER SUPPLIER

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to the field of power conversion, and more particularly, to a voltage converter circuit, a controlling method and a power supplier.

BACKGROUND

This section introduces aspects that may facilitate better understanding of the present disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the related art.

In the field of power conversion, a switching element in a voltage converter maybe controlled to be switched on or off, so that an input DC (direct current) voltage is converted into an output DC voltage. The input voltage and the output voltage may be different, and the output voltage may be changed according to the switching frequency and duty ratio of a controlling signal that controls the switching element.

A bootstrap gate driver may be applied in the voltage converter, to provide a relatively higher driving voltage to the switching element. For example, the voltage converter may be a buck converter.

Fig. 1 is a diagram of a buck converter. As shown in Fig. 1, the buck converter includes a bootstrap gate driver 101, a bootstrap capacitor C _BOOT, and a converting circuit 103.

The bootstrap gate driver 101 outputs a driving signal from a first output port Ho, according to a controlling signal received from a first input port IN. The controlling signal may be a PWM (Pulse Width Modulation) signal, which may be generated by a controller. The supply voltage input port V _DD receives a supply voltage, for example, the supply voltage is 15V.

As shown in Fig. 1, the bootstrap capacitor C _BOOT is connected between a second output port V _B and a third output port V _S of the bootstrap gate driver 101.

The converting circuit 103 includes at least a first switching element Q1, an inductor L1 and a capacitor C2 connecting in serial between an input voltage port and a ground port GND. An input voltage V _IN is received from the input voltage port. An output voltage V _OUT is outputted from an output voltage port, which connects to a first connecting node A between the inductor L1 and the capacitor C2. A gate of the first switching element Q1 connects to the first output port Ho, and receives the driving signal.

As shown in Fig. 1, the third output port V _S is connected to a connecting node B between the inductor L1 and the switching element Q1. When voltage of the third output port V _S is lower than the supply voltage, the supply voltage may charge the bootstrap capacitor C _BOOT through a bootstrap resistor R _BOOT and a bootstrap diode D _BOOT, so that the voltage at the second output port V _B is high level.

As shown in Fig. 1, when the controlling signal is low level, the first output port Ho outputs the driving voltage of low level, and the switching element Q1 is turned off. When the controlling signal is high level, the first output port Ho outputs the driving voltage of high level, which is provided by voltage at the second output port V _B, thus the switching element Q1 is turned on. Hence, with the operation of the switching element, the input voltage V _IN is converted into the output voltage V _OUT.

SUMMARY

Inventors of this disclosure found:

As shown in FIG. 1, at the mains fast switching condition, especially when the output voltage V _OUT is high enough, the voltage of the second output port Vs may be higher than the supply voltage, hence the bootstrap capacitor C _BOOT will not be charged by the supply voltage, and the driving voltage outputted from the first output port Ho may not be high enough to turn on the switching element Q1. Therefore, the voltage converter maybe latched or the startup time will be very long, and the converter will not normally operate until the output voltage discharged to a low level.

In general, embodiments of the present disclosure provide a voltage converter circuit, a controlling method and a power supplier. In the embodiments, the third output port Vs may disconnects from the output voltage, when the voltage on the bootstrap capacitor C _BOOT is lower than a predetermined value. Therefore, the bootstrap capacitor C _BOOT will be charged up in a short time, and the voltage converter circuit will not be latched and will startup soon, even at the mains fast switching condition.

In a first aspect, there is provided a voltage converter circuit, includes: a bootstrap gate driver, configured to output a driving signal from a first output port (Ho) according to a controlling signal received from a first input port; a bootstrap capacitor, configured to be connected between a second output port (Vb) and a third output port (Vs) of the bootstrap gate driver; a converting circuit, configured to include at least a first switching element, an inductor and a capacitor connecting in serial between an input voltage port and a ground port, an output voltage being outputted from an output voltage port which connects to a first connecting node (A) between the inductor and the capacitor, a gate of the first switching element receives the driving signal; and a first connecting control circuit, configured to be connected between the third output port (Vs) and a second connecting node (B) between the first switching element and the inductor, , the first connecting control circuit controls the second connecting node to electrically connect to or disconnect from the third output port, according to a voltage of the second output port.

In an embodiment, when the voltage of the second output port is lower than a predetermined value, the first connecting control circuit controls the second connecting node to electrically disconnect from the third output port.

In an embodiment, when the voltage of the second output port is equal to or higher than the predetermined value, the first connecting control circuit controls the second connecting node to electrically connect to the third output port.

In an embodiment, when the voltage of the second output port is equal to or higher than the predetermined value, the driving signal turns on the first switching element, when the controlling signal is at a high level.

In an embodiment, the first connecting control circuit includes:

a resistor string, configured to include at least two resistors which are connected in serial between the second output port (Vb) and the third output port (Vs) ; a second switching element, configured to be connected between the second connecting node (B) and the third output port (Vs) , a gate of the second switching element is connected to a third connecting node (C) between two resistors of the resistor string.

In an embodiment, when the voltage of the second output port is lower than the predetermined value, the second switching element is turned off, and the second connecting node electrically disconnects from the third output port.

In an embodiment, when the voltage of the second output port is equal to or higher than the predetermined value, the second switching element is turned on, and the second connecting node electrically connects to the third output port.

In an embodiment, the voltage converter circuit further includes: a second connecting control circuit, configured to be connected between the third output port (Vs) and the ground port, the second connecting control circuit controls the third output port (Vs) to electrically connect to or disconnect from the ground port, according to the controlling signal.

In an embodiment, when the controlling signal is at a high level, the second connecting control circuit controls the third output port (Vs) to electrically disconnect from the ground port; when the controlling signal is at a low level, the second connecting control circuit controls the third output port (Vs) to electrically connect to the ground port.

In a second aspect, there is provided a power supplier, including a controller, and the voltage converter circuit according to the first aspect, the controller is configured to generate the controlling signal, and send the controlling signal to the first input port of the bootstrap gate driver of the voltage converter circuit; the voltage converter circuit is configured to convert an input voltage at the input voltage port into the output voltage, according to the controlling signal.

In a third aspect, there is provided a controlling method of a voltage converter circuit, the method including:

a bootstrap gate driver outputs a driving signal from a first output port (Ho) according to a controlling signal received from a first input port, a bootstrap capacitor being connected between a second output port (Vb) and a third output port (Vs) of the bootstrap gate driver;

a converting circuit converts an input voltage into an output voltage according to the controlling signal, the converting circuit including at least a first switching element, an inductor and a capacitor connecting in serial between an input voltage port and a ground port, the output voltage being outputted from an output voltage port which connects to a first connecting node (A) between the inductor and the capacitor, a gate of the first switching element receiving the driving signal; and

a first connecting control circuit controls the second connecting node to electrically connect to or disconnect from the third output port, according to a voltage of the second output port, the first connecting control circuit being connected between the third output port (Vs) and a second connecting node (B) between the first switching element and the inductor.

According to various embodiments of the present disclosure, the bootstrap capacitor will be charged up in a short time, and the voltage converter circuit will not be latched and startup soon.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and benefits of various embodiments of the disclosure will become more fully apparent, by way of example, from the following detailed description with reference to the accompanying drawings, in which like reference numerals or letters are used to designate like or equivalent elements. The drawings are illustrated for facilitating better understanding of the embodiments of the disclosure and not necessarily drawn to scale, in which:

Fig. 1 is a diagram of a buck converter;

Fig. 2 is a diagram of a voltage converter circuit in accordance with an embodiment of the present disclosure;

Fig. 3 shows a flowchart of a controlling method 300 of the voltage converter circuit.

DETAILED DESCRIPTION

The present disclosure will now be discussed with reference to several example embodiments. It should be understood that these embodiments are discussed only for the purpose of enabling those skilled persons in the art to better understand and thus implement the present disclosure, rather than suggesting any limitations on the scope of the present disclosure.

As used herein, the terms “first” and “second” refer to different elements. The singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises, ” “comprising, ” “has, ” “having, ” “includes” and/or “including” as used herein, specify the presence of stated features, elements, and/or components and the like, but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof. The term “based on” is to be read as “based at least in part on. ” The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment. ” The term “another embodiment” is to be read as “at least one other embodiment. ” Other definitions, explicit and implicit, may be included below.

In the description and drawings, particular embodiments of the disclosure have been disclosed in detail as being indicative of some of the ways in which the principles of the disclosure may be employed, but it is understood that the disclosure is not limited correspondingly in scope. Rather, the disclosure includes all changes, modifications and equivalents coming within the spirit and terms of the appended claims.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. To facilitate illustrating and describing some parts of the disclosure, corresponding portions of the drawings may be exaggerated in size, e.g., made larger in relation to other parts than in an exemplary device actually made according to the disclosure. Elements and features depicted in one drawing or embodiment of the disclosure may be combined with elements and features depicted in one or more additional drawings or embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views and may be used to designate like or similar parts in more than one embodiment.

First aspect of embodiments

A voltage converter circuit is provided in a first embodiment.

Fig. 2 is a diagram of a voltage converter circuit in accordance with an embodiment of the present disclosure. As shown in Fig. 2, the voltage converter circuit 200 includes a bootstrap gate driver 201, a bootstrap capacitor C81, converting circuit 202, and a first connecting control circuit 203.

The bootstrap gate driver 201 outputs a driving signal from a first output port Ho (pin number 7) , according to a controlling signal received from a first input port IN (pin number 2) . The controlling signal may be a PWM (Pulse Width Modulation) signal, which may be generated by a controller. The supply voltage input port V _DD (pin number 1) receives a supply voltage, for example, the supply voltage is 15V.

As shown in Fig. 2, the bootstrap capacitor C81 is connected between a second output port V _B (pin number 8) and a third output port V _S (pin number 6) of the bootstrap gate driver 201.

The converting circuit 202 includes at least a first switching element M70, an inductor L71 and a capacitor C73, connecting in serial between an input voltage port 203 and a ground port GND (pin number 4) .

In the embodiment, an input voltage V _IN is received from the input voltage port 204. An output voltage V _OUT is outputted from an output voltage port 205, which connects to a first connecting node A between the inductor L71 and the capacitor C73. A gate of the first switching element M70 may connect to the first output port Ho, and receives the driving signal.

As shown in Fig. 2, when the controlling signal is low level, the first output port Ho may output the driving voltage of low level, and the first switching element M70 may be turned off. When the controlling signal is high level, the first output port Ho may output the driving voltage of high level, which is provided by voltage at the second output port Vb, thus the first switching element M70 is turned on. Hence, with the operation of the first switching element, the input voltage V _IN is converted into the output voltage V _OUT.

As shown in Fig. 2, the first connecting control circuit 203 may be connected between the third output port Vs and a second connecting node B between the first switching element M70 and the inductor L71.

In the embodiment, the first connecting control circuit 203 may control the second connecting node B to electrically connect to or disconnect from the third output port Vs, according to a voltage of the second output port Vb. Therefore, a connecting state between the second connecting node B and the third output port Vs may be switched, and the affect that the output voltage V _OUT produced on the charging up of the bootstrap capacitor C81 may be reduced.

For one example, when the voltage of the second output port Vb is equal to or higher than the predetermined value, the first connecting control circuit 203 may control the second connecting node B to electrically connect to the third output port, and the first switching element M70 may be turned on by the high level driving signal. That is, when the voltage of the second output port is equal to or higher than the predetermined value, the driving signal may turn on the first switching element M70 when the controlling signal is at a high level.

For another example, when the voltage of the second output port Vb is lower than a predetermined value, the first connecting control circuit 203 may control the second connecting node B to electrically disconnect from the third output port Vs. Hence, the voltage at the third output port Vs may discharge to be low level, and the supply voltage may charge up the bootstrap capacitor C81 through a bootstrap resistor R91 and a bootstrap diode D72 in a short time, so that the voltage at the second output port Vb is high level. Therefore, the voltage converter circuit 200 will not be latched and will start up soon, even at the mains fast switching condition.

As shown in FIG. 2, the first connecting control circuit 203 includes a resistor string, and a second switching element M95.

In the embodiment, the resistor string may include at least two resistors R95 and R96, which are connected in serial between the second output port Vb and the third output port Vs.

In the embodiment, the second switching element M95 may be connected between the second connecting node B and the third output port Vs. A gate of the second switching element M95 is connected to a third connecting node C between two resistors R95 and R96 of the resistor string.

As shown in FIG. 2, when the voltage of the second output port Vb is lower than the predetermined value, the second switching element M95 is turned off, and the second connecting node B electrically disconnects from the third output port Vs. Therefore, the voltage of the third output port Vs will not be affected by the output voltage V _OUT, even when the output voltage V _OUT is high, the bootstrap capacitor C81 can be charged up in a short time.

In the embodiment, when the voltage of the second output port is equal to or higher than the predetermined value, the second switching element is turned on, the second connecting node B electrically connects to the third output port Vs, and the voltage converter circuit may normally operate.

In the embodiment, FIG. 2 shows an example of the first connecting control circuit 203. However, the embodiment is not limited there to, the first connecting control circuit 203 may be other type.

In the embodiment, the first switching element M70 may be N-channel MOS (Metal Oxide Semiconductor) transistor. The second switching element M95 may be N-channel MOS transistor, however, the second switching element M95 may be other type of transistor, such as bipolar transistor.

As shown in FIG. 2 the voltage converter circuit may further include a second connecting control circuit 206. The second connecting control circuit 206 may be connected between the third output port Vs and the ground port. The second connecting control circuit 206 may control the third output port Vs to electrically connect to or disconnect from the ground port, according to the controlling signal.

For example, when the controlling signal is at a high level, the second connecting control circuit 206 may control the third output port Vs to electrically disconnect from the ground port. When the controlling signal is at a low level, the second connecting control circuit 206 may control the third output port Vs to electrically connect to the ground port.

As shown in FIG. 2, the second connecting control circuit 206 may include a third switching element Q70 and a fourth switching element M71. The third switching element Q70 may be an NPN bipolar transistor, and the fourth switching element M71 may be an N-channel MOS transistor.

In the embodiment, a base electrode of the third switching element Q70 connects to the supply voltage through a resistor R92, a resistor R70 and the bootstrap resistor R91. A collector electrode of Q70 connects to the third output port Vs through a resistor R72 and a resistor R73. An emitter electrode of Q70 connects to the ground port.

In the embodiment, a drain of the fourth switching element M71 connects to the base electrode of Q70 through the resistor R92. A source of the fourth switching element M71 connects to the ground port. A gate of the fourth switching element M71 receives the controlling signal through a resistor R93. A resistor R94 connects between the gate of M71 and the ground port.

In the embodiment, when the controlling signal is at a high level, the fourth switching element M71 is turned on, and the third switching element Q70 is turned off. Hence, and the third output port Vs electrically disconnects from the ground port.

In the embodiment, when the controlling signal is at a low level, the fourth switching element M71 is turned off, and the third switching element Q70 is turned on by the supply voltage. Hence, the third output port Vs electrically connects to the ground port, and the voltage at the third output port Vs is getting low level.

In the embodiment, the third switching element Q70 may be an NPN bipolar transistor, and the fourth switching element M71 may be an N-channel MOS transistor. However, the third switching element Q70 and the fourth switching element M71 may be other type of transistors.

As shown in FIG. 2, the bootstrap gate driver 201 may be integrated circuit, for example, FAN7371 made Fairchild Semiconductor Corporation. The pins of number 3 and number 5 may connect to no element.

As shown in FIG. 2, the voltage converter circuit 201 may further include other elements, which are shown in FIG. 2, and their values are also listed. The function and working principle of these elements may be referred to the related art.

In the embodiment, the third output port Vs may disconnects from the output voltage, when the voltage on the bootstrap capacitor C _BOOT is lower than a predetermined value. Therefore, the bootstrap capacitor C _BOOT will be charged up in a short time, and the voltage converter circuit will not be latched and will startup soon, even at the mains fast switching condition.

Second aspect of embodiments

A controlling method of a voltage converter circuit of the first aspect of embodiments is provided in an embodiment. The same contents as those in the first aspect of embodiments are omitted.

As shown in Fig. 3, the method 300 includes:

Block 301: a bootstrap gate driver outputting a driving signal from a first output port (Ho) according to a controlling signal received from a first input port;

Block 302: a converting circuit converting an input voltage into an output voltage according to the controlling signal;

Block 303: a first connecting control circuit controlling the second connecting node to electrically connect to or disconnect from the third output port, according to a voltage of the second output port.

In the block 303, when the voltage of the second output port is lower than a predetermined value, the first connecting control circuit controls the second connecting node to electrically disconnect from the third output port. When the voltage of the second output port is equal to or higher than a predetermined value, the first connecting control circuit controls the second connecting node to electrically connect to the third output port.

As shown in Fig. 3, the method 300 further includes:

Block 304: a second connecting control circuit controls the third output port to electrically connect to or disconnect from the ground port, according to the controlling signal.

In the block 304, when the controlling signal is at a high level, the second connecting control circuit controls the third output port (Vs) to electrically disconnect from the ground port. When the controlling signal is at a low level, the second connecting control circuit controls the third output port (Vs) to electrically connect to the ground port.

As can be seen from the above embodiments, the third output port Vs may disconnects from the output voltage, when the voltage on the bootstrap capacitor C _BOOT is lower than a predetermined value. Therefore, the bootstrap capacitor C _BOOT will be charged up in a short time, and the voltage converter circuit will not be latched and will startup soon, even at the mains fast switching condition.

Third aspect of embodiments

A power supplier is provided in an embodiment. The power supplier includes a controller, and the voltage converter circuit according to the first aspect of embodiments.

In the embodiment, the controller is configured to generate the controlling signal, and send the controlling signal to the first input port of the bootstrap gate driver of the voltage converter circuit.

In the embodiment, the voltage converter circuit is configured to convert an input voltage at the input voltage port into the output voltage, according to the controlling signal, as described in the first aspect of embodiments.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in language specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A voltage converter circuit, comprising:

a bootstrap gate driver, configured to output a driving signal from a first output port (Ho) according to a controlling signal received from a first input port;

a bootstrap capacitor, configured to be connected between a second output port (Vb) and a third output port (Vs) of the bootstrap gate driver;

a converting circuit, configured to comprise at least a first switching element, an inductor and a capacitor connecting in serial between an input voltage port and a ground port, wherein, an output voltage being outputted from an output voltage port which connects to a first connecting node (A) between the inductor and the capacitor, a gate of the first switching element receives the driving signal; and

a first connecting control circuit, configured to be connected between the third output port (Vs) and a second connecting node (B) between the first switching element and the inductor, wherein, the first connecting control circuit controls the second connecting node to electrically connect to or disconnect from the third output port, according to a voltage of the second output port.
The voltage converter circuit according to claim 1, wherein,

when the voltage of the second output port is lower than a predetermined value, the first connecting control circuit controls the second connecting node to electrically disconnect from the third output port.
The voltage converter circuit according to claim 2, wherein,

when the voltage of the second output port is equal to or higher than the predetermined value, the first connecting control circuit controls the second connecting node to electrically connect to the third output port.
The voltage converter circuit according to claim 2, wherein,

when the voltage of the second output port is equal to or higher than the predetermined value,

the driving signal turns on the first switching element, when the controlling signal is at a high level.
The voltage converter circuit according to claim 2, wherein, the first connecting control circuit comprises:

a resistor string, configured to comprise at least two resistors which are connected in serial between the second output port (Vb) and the third output port (Vs) ;

a second switching element, configured to be connected between the second connecting node (B) and the third output port (Vs) , a gate of the second switching element is connected to a third connecting node (C) between two resistors of the resistor string.
The voltage converter circuit according to claim 5, wherein,

when the voltage of the second output port is lower than the predetermined value, the second switching element is turned off, and the second connecting node electrically disconnects from the third output port.
The voltage converter circuit according to claim 5, wherein,

when the voltage of the second output port is equal to or higher than the predetermined value, the second switching element is turned on, and the second connecting node electrically connects to the third output port.
The voltage converter circuit according to claim 1, wherein, the voltage converter circuit further comprises:

a second connecting control circuit, configured to be connected between the third output port (Vs) and the ground port,

wherein, the second connecting control circuit controls the third output port (Vs) to electrically connect to or disconnect from the ground port, according to the controlling signal.
The voltage converter circuit according to claim 1, wherein,

when the controlling signal is at a high level, the second connecting control circuit controls the third output port (Vs) to electrically disconnect from the ground port;

when the controlling signal is at a low level, the second connecting control circuit controls the third output port (Vs) to electrically connect to the ground port.
A power supplier, comprising a controller, and the voltage converter circuit according to one of claims 1-9, wherein:

the controller is configured to generate the controlling signal, and send the controlling signal to the first input port of the bootstrap gate driver of the voltage converter circuit;

the voltage converter circuit is configured to convert an input voltage at the input voltage port into the output voltage, according to the controlling signal.
A controlling method of a voltage converter circuit, the method comprising:

a bootstrap gate driver outputting a driving signal from a first output port (Ho) according to a controlling signal received from a first input port, wherein, a bootstrap capacitor being connected between a second output port (Vb) and a third output port (Vs) of the bootstrap gate driver;

a converting circuit converting an input voltage into an output voltage according to the controlling signal, wherein the converting circuit comprising at least a first switching element, an inductor and a capacitor connecting in serial between an input voltage port and a ground port, the output voltage being outputted from an output voltage port which connects to a first connecting node (A) between the inductor and the capacitor, a gate of the first switching element receiving the driving signal; and

a first connecting control circuit controlling the second connecting node to electrically connect to or disconnect from the third output port, according to a voltage of the second output port, wherein the first connecting control circuit being connected between the third output port (Vs) and a second connecting node (B) between the first switching element and the inductor.
The method according to claim 11, wherein,

when the voltage of the second output port is lower than a predetermined value, the first connecting control circuit controls the second connecting node to electrically disconnect from the third output port.